(1) Field of the Invention
The present invention relates to a catalyst for steam reforming of methanol which can be used to obtain hydrogen by decomposing methanol in the presence of steam, and to a method for producing hydrogen with the catalyst.
(2) Description of the Prior Art
Conventionally, there have been proposed, as catalysts for steam reforming of methanol, a number of catalysts having platinum or palladium supported on carriers such as alumina, or alternatively having a carried base metal like copper, nickel, chromium, zinc, or the like.
In general, it is commonly known that catalysts formed of element(s) of the copper group have excellent activity and selectivity (xe2x80x9cShokubai Koza (Catalysis Course), vol. 9,xe2x80x9d edited by the Catalysis Society of Japan (published on May 10, 1985), Kodansha Ltd., pp. 132-134). On the other hand, it is believed that these catalysts formed of element(s) of the copper group, although they are excellent in activities, have problems in terms of heat stability.
Catalysts formed of copper compounds further containing palladium or platinum element are known, for example, there are disclosed catalysts having zinc, chromium, as a major component, and containing any one of copper, cobalt, platinum, palladium, rhodium, nickel, manganese, magnesium, and molybdenum (Japanese Patent Laid-Open No. 57-56302).
In addition, with respect to catalysts having a small deterioration of activity at elevated temperatures and showing a high catalytic activity, there are known methods in which the activity can be improved by supporting one or more metals from the group consisting of copper, zinc, chromium, and nickel and one or more metals from the group consisting of platinum and palladium on a carrier, alumina pre-coated with zirconia (Japanese Patent Laid-Open No. 57-7255).
As methods for preparing catalysts with superior activity and stability, there are known methods of preparing catalysts containing at least one metal of copper, zinc, aluminum and rare metals, and zirconium and further containing at least one metal selected from palladium, silver, rhenium and platinum (Japanese Patent Laid-Open No. 60-209255).
Furthermore, with respect to catalysts having high durability, there are known ones composed of metal oxide having, as essential components, copper oxide, zinc oxide, aluminum oxide, and silicon oxide, which may contain zirconium oxide, gallium oxide, palladium oxide as an optional component (Japanese Patent Laid-Open No. 10-309466).
As described above, although there are many known catalysts containing copper and platinum, and palladium, such catalysts are limited to ones having a range of relatively high atomic ratios of copper to platinum, palladium.
As general methods for preparing copper-based catalysts, kneading, coprecipitating, Cu plating, Cu spray coating methods, and the like are known, which methods have limitations on the minimum particle size of the catalysts. As catalysts displaying superior activity and durability, alloy-based catalysts of ultrafine particles are disclosed (Japanese Patent Laid-Open Nos. 07-116517, 07-265704, 08-215571, and 08-215576).
However, in all of the known methods mentioned above, it is at the actual circumstance that there exists no method having sufficient properties in terms of both activity and durability.
The present invention is intended to solve the disadvantages of catalysts hitherto known, thereby providing a new catalyst for steam reforming of methanol which can provide both sufficient catalyst activity and durability, and further providing an efficient method for producing hydrogen with the catalyst.
The inventors have conducted extensive research to solve the above-mentioned problems. In consequent, the inventor have found that the improvement in not only durability but also catalyst activity can be obtained surprisingly by adding palladium and/or platinum element(s), which have conventionally displayed an extremely low activity when used alone, to copper- and zinc-based catalysts in large amounts. On the basis of such findings, the present invention has been made.
The present invention is specified by the followings.
[1] A catalyst for steam reforming of methanol, characterized by comprising copper and zinc, and palladium and/or platinum, and in that an atomic ratio of copper to palladium and/or platinum is 0.5 to 10 and an atomic ratio of zinc to copper is 0.1 to 10.
[2] The catalyst for steam reforming of methanol according to [1], characterized in that the catalyst comprises palladium and/or platinum and the atomic ratio of copper to palladium and/or platinum is 0.5 to 5.
[3] The catalyst for steam reforming of methanol according to [1], characterized in that the catalyst comprises palladium and/or platinum and the atomic ratio of copper to palladium and/or platinum is 0.5 to 3.
[4] The catalyst for steam reforming of methanol according to any one of [1] to [3], characterized in that a catalyst comprising copper and zinc, and palladium and/or platinum is prepared by a coprecipitation method and subjected to calcining at 200xc2x0 C. to 470xc2x0 C.
[5] A method for producing hydrogen, characterized in that methanol is subjected to steam reforming in the presence of the catalyst according to any one of [1] to [4].